A motion guide apparatus that guides the linear motion of a mobile body such as a table using the rolling motion of rolling elements is known. The motion guide apparatus is also called a linear guide, and includes a track rail, and a moving block assembled in a movable manner to the track rail via rolling elements. A rolling element rolling portion where the rolling elements can make a rolling motion is formed along a longitudinal direction in the track rail. A circulation path for circulating the rolling elements is formed in the moving member. The circulation path includes a loaded rolling element rolling portion facing the rolling element rolling portion of the track rail, a return path parallel to the loaded rolling element rolling portion, and a pair of U-shaped direction changing paths linking one end and the other end of the return path.
A typical motion guide apparatus is formed by assembling end caps to both end surfaces in a movement direction of a moving block body. The moving block body includes a central portion facing an upper surface of the track rail, and a pair of sleeve portions facing side surfaces of the track rail, and is formed in an angular U shape. The loaded rolling element rolling portion of the circulation path is formed on an inner side surface of the sleeve portion of the moving block body. An inner peripheral side of the direction changing path is formed into a semi-cylindrical portion that is also called an R piece. An outer peripheral side of the direction changing path is formed in the end cap. After the R piece is incorporated into the end cap, the end cap is attached to the end surface in the movement direction of the moving member body to form the circulation path.
When the rolling elements are loaded into the circulation path, the rolling elements are loaded from an inner side surface of the angular U-shaped moving block body. However, the rolling element loading operation is an operation in a small space; therefore, there is a problem that it takes time and trouble. In order to solve this problem, an invention has been proposed in which an end cap is provided with an opening to insert rolling elements from the opening toward a longitudinal direction of a track rail (see Patent Literature 1). After the rolling elements are loaded into a circulation path, the opening is closed with a closing member. According to this invention, the rolling elements can be loaded using a large space in a longitudinal direction of a track rail; accordingly, the loading operation is facilitated. A motion guide apparatus especially suitable for automatic loading of rolling elements by an automatic machine can be obtained.